The goal of this Program Announcement (PA) is to promote the identification of susceptibility genes for complex neurological and neurobehavioral disorders. For this PA, complex disorders are defined as those caused by the interaction of multiple genes, or by a combination of genetic and environmental risk factors. Many of these disorders are relatively common and clinically heterogeneous. Projects focusing on any phase of the gene discovery process, from initial patient ascertainment to positional cloning, are appropriate. Novel approaches, including the use of intermediate phenotypes that potentially underlie complex disorders, are also encouraged.